Driver side or passenger side supplemental inflatable restraint (SIR) systems typically include an air bag stored in a housing module within the interior of the vehicle in close proximity to either the driver or one or more passengers. SIR systems are designed to actuate upon sudden deceleration to rapidly deploy an air bag to restrain the movement of the driver or passengers. During deployment, gas is emitted rapidly from an inflator, which produces gas to expand the air bag cushion to a fully inflated state.
Known inflators for air bag cushions are generally of three types. One type is the pure gas inflator wherein a pressure vessel contains stored pressurized gas. The pressure vessel communicates with the cushion through various types of rupturable outlets or diaphragms. Another type is the gas generator wherein a propellant is ignited and the resultant gases flow through an outlet to the cushion. A third type is the hybrid or augmented type. This type includes a pressure vessel containing stored pressurized gas and a gas generator. When the generator is ignited, the resultant gas flows with the stored gas to the cushion through the pressure vessel outlet.
It is also known to inflate the cushion at a relatively low rate under low level deployment conditions, such as a sudden low level deceleration, and at a relatively high rate under high level deployment conditions, such as a sudden high level deceleration. This can be accomplished in a pure gas type inflator by providing the pressure vessel with an outlet of variable flow area. In addition, devices are known which provide primary inflation (reduced inflation) and full level inflation using a single gas vessel with two separate gas heaters. Primary inflation is accomplished by actuating the gas vessel and heating the gas at a specified reduced level. Full level inflation is accomplished by actuating a second separate heater located at the bottom of the gas vessel to heat the gas at a greater level. This second heater is deployed at the same time or a delayed time as the primary heater to provide full level inflation.
It is also known in the art to use a system having two discrete inflators to accomplish dual level inflation. In these types of systems, two discrete inflators are deployed at the same time or at a delayed time depending upon the severity of the sudden deceleration.